1. Field of the Invention
The present invention relates to a coil component, particularly to a coil component that is suitably used as a coupled inductor of a power-supply device. The invention also relates to a power-supply device provided with the coil component.
2. Description of Related Art
A so-called multi-phase regulator circuit is known as one of power-supply devices used in a computer and the like. In the multi-phase regulator circuit, switching currents having different phases are produced by switching, and a smooth output current is obtained by combining the switching currents. In the multi-phase regulator circuit, a coil component called a coupled inductor may be used in order to smooth output current. For example, Japanese Patent Application Laid-Open No. 2007-184509 discloses a coupled inductor.
In order to smooth output current by the coupled inductor, it is necessary that a magnetic coupling be generated at a desired level between a pair of conductors through which the switching currents are passed. That is, the smooth output current cannot be obtained, when the excessively strong magnetic coupling is generated between the conductors, or when the excessively weak magnetic coupling is generated between the conductors. Therefore, it is necessary to adjust the magnetic coupling to an optimum level. The magnetic coupling level can be adjusted by changing a thickness or a shape of a magnetic body existing between the conductors. Specifically, as illustrated in FIG. 12A, grooves 11 and 12 in which the conductors (not illustrated) are disposed are formed in a magnetic core 10, and the grooves 11 and 12 are completely separated by a partition wall 13 that is a part of the magnetic core 10, thereby reducing the magnetic coupling between the conductors. On the other hand, as illustrated in FIG. 12B, when the grooves 11 and 12 are integrated by removing the partition wall 13, the magnetic coupling between the conductors is increased.
However, when the target magnetic coupling level is larger than the level obtained by the structure of FIG. 12A and smaller than the level obtained by the structure of FIG. 12B, the magnetic coupling is hardly adjusted by the presence or absence of the partition wall 13. As illustrated in FIG. 12C, the grooves 11 and 12 may be partially connected through a cavity 13a by removing a part of the partition wall 13. In this case, an intermediate level between the magnetic coupling level obtained by the structure of FIG. 12A and the magnetic coupling level obtained by the structure of FIG. 12B can be obtained. Accordingly, it is believed that a desired magnetic coupling can be obtained by adjusting a length L of the cavity 13a. 
However, according to the research of the inventors, it is proved that various problems occur when the magnetic coupling is adjusted only by the length L of the cavity 13a. Specifically, when the length L of the cavity 13a is increased to enhance the magnetic coupling, a volume of the cavity 13a is increased with the length. That is, the large cavity exists in the magnetic core 10. On the other hand, because a predetermined volume (core volume) is required for the magnetic core 10, external dimensions of the magnetic core 10 are to be enlarged when the large cavity exists in the magnetic core 10.
In order to enhance the magnetic coupling without enlarging the external dimensions of the magnetic core 10, a distance (a thickness T of the partition wall 13) between the grooves 11 and 12 may be shorten. However, a distance between the conductors is also shortened when the distance between the grooves 11 and 12 is shortened, which increases a risk of a short circuit failure between terminal electrodes. Such problems are not significant in the coupled inductor in which the coated lead wire is installed in the groove like the coupled inductor disclosed in Japanese Patent Application Laid-Open No. 2007-184509. On the other hand, such problems become significant in the coupled inductor in which the end portions of the conductors disposed in the grooves 11 and 12 are used as the terminal electrode like a surface-mounted coupled inductor.
The problems occur in not only the coupled inductor but also the overall coil component.